The use of bitumen in the production of materials for highway and industrial applications has been known for a long time: bitumen is the main hydrocarbon binder used in the field of road construction or civil engineering. To be able to be used as a binder in these different applications, the bitumen must have certain mechanical properties, in particular elastic or cohesive properties. Since bitumen on its own is generally not sufficiently elastic or cohesive, polymers are added which can optionally be crosslinked. These polymers, crosslinked or not, provide improved elastic and cohesive properties to the bitumen/polymer. Generally, the crosslinking is irreversible; once the crosslinking has been carried out, it is not possible to return to the initial state existing before the crosslinking reaction. Crosslinked bitumen/polymer compositions thus have good mechanical properties, but their viscosity is very high. In fact, the two characteristics “mechanical properties” on the one hand, and “fluidity” on the other hand, are contradictory. The mechanical properties (elasticity and cohesion), are promoted by long chain lengths, therefore by crosslinking of the polymer chains. Fluidity is promoted by a short chain length, therefore by an absence of crosslinking or a weak crosslinking of the polymer chains. According to the applications envisaged, it is necessary to find a good compromise between mechanical properties and fluidity by adjusting the rate or the nature of the crosslinking.